The present invention relates to an antilock control method in which during the running of an automotive vehicle on a road surface (.mu.-split surface) having a different coefficient of friction where one of the right and left wheels of the same axle is on a road surface of the higher coefficient of friction and the other one of the wheels is on a road surface of the lower coefficient of friction, when the brake is operated and an antilock control starts, the braking force difference between the right and left front-wheels is reduced, thereby improving the vehicle stability and making the steering maneuver by the driver easy.
When the running vehicle abruptly brakes, the wheel of the vehicle is locked and skids since there is a limit of frictional force between the wheel and the road surface.
For the means to prevent the wheel locking phenomenon, there has been known a conventional antilock control system which controls a slip rate of the wheel on the road surface so as to be constant.
In the vehicle equipped with the antilock control system, when one of the wheels of the same axle runs on the surface having the lower coefficient of friction (referred to as a low-.mu. load surface), e.g., an ice road surface, if the wheels are controlled so that the slip rate of one of those wheels is equal to that of the other one, a braking force to the wheel on the road surface having the higher coefficient of friction (referred to as a high-.mu. road surface) becomes larger than that of the wheel on the low-.mu. load surface, so that the vehicle possibly spins. Particularly in those vehicles, e.g., the short-wheel base vehicle, the high gravity-center vehicle, the vehicle having a large scrub radius, the vehicle will more easily spin.
The solution to this problem is proposed: when the wheel on the low u road surface (select low) is locked, the hydraulic braking pressure to the wheel on the high .mu. road surface (referred to frequently as a "high .mu. road side wheel") is forcibly decreased in accordance with the hydraulic braking pressure to the wheel on the low .mu. road surface (referred to frequently as a low .mu. road side wheel) (select low), as disclosed in Japanese Patent Laid-Open Publication No. Sho. 63-170154.
The proposed solution in which the brake pressure to the high .mu. road side wheel is controlled with respect to a state of the low .mu. road side wheel (select low), has the following problem, however. When the low .mu. road side wheel (select low) slips, the hydraulic braking pressure to the high .mu. road side wheel is also forcibly reduced in synchronism with the slippage. Therefore, it is impossible to efficiently utilize the braking force to the wheel on the high .mu. road side wheel. In other words, an efficiency of the utilization of the road surface on which the high .mu. road side wheel runs is reduced, so that the stopping distance is long.